Under certain circumstances, it can be desirable to provide a plurality of power supplies connected in parallel so as to have a common output node for supplying power to a load. If each power supply were to operate independently, however, a disproportionate amount of the current required by the load would tend to be supplied by only one power supply while the other power supplies would supply significantly less current. FIG. 1 shows a parallel operation of an uninterruptible power supply system according to the prior art. Please refer to FIG. 1. A typical parallel operation of an uninterruptible power supply (UPS) system must use a set of parallel-linking inductors L1, L2, . . . , Ln connected in parallel so as to stabilize the output voltage thereof In order to stabilize the output voltage of the system, it is necessary to utilize large inductors to stabilize the output voltage thereof. The technique has disadvantages in which the efficiency of the system is reduced, the volume of the system is increased, and the product cost is increased.
It is therefore attempted by the applicant to deal with the above situation encountered with the prior art.